Conventionally, as the linear guide device constituting a linear guide portion of the machine tool or various industrial robots, there is known a device composed of a linear track rail on which a ball rolling surface is formed along a longitudinal direction thereof and a slider attached to the track rail through intermediation of a plurality of balls. The slider includes a load rolling surface opposed to the ball rolling surface of the track rail, and a circulation passage allowing endless circulation of the plurality of balls rolling while being applied with load between the load rolling surface and the rolling surface of the track rail. By allowing the balls to circulate in the endless circulation passage, the slider can continuously move in an overall length of the track rail.
Normally, the track rail is fixed to a base portion such as a bed or a column of the machine tool or the like by fastening fixing bolts. Therefore, rail mounting holes for allowing the fixing bolts to pass therethrough are formed to pass through the track rail at predetermined intervals along the longitudinal direction thereof. A head portion of the fixing bolt protruding on the track rail becomes an obstacle to movement of the slider along the track rail, so an inner portion of the rail mounting hole is divided into two sections including a small diameter portion and a large diameter portion. The small diameter portion has an inner diameter which is slightly larger than a nominal diameter of the bolt. The large diameter portion has an inner diameter which is slightly larger than the head portion of the bolt. That is, the large diameter portion constitutes an accommodation portion for the bolt head portion, thereby preventing the bolt head portion from protruding on a surface of the track rail.
However, the rail mounting hole becomes a cause of entry of a foreign substance such as shaving of a work or a coolant liquid in the machine tool into an inside of the slider moving along the track rail. In the slider, the balls circulate while being applied with a load between the slider and the track rail. When the foreign substance such as shaving of a work or refuse enters the inside of the slider, scars are generated on the rolling surface of the track rail and the balls on the load rolling surface of the slider, or wear of those is promoted, thereby causing movement accuracy of the slider in the linear guide device to be impaired early. When the coolant liquid used for cooling a work in the machine tool enters the inside of the slider, lubricating oil adhering to surfaces of the balls is washed away, thereby causing early wear of the rolling surface and the balls as well. In order to prevent the foreign substance from entering the inside of the slider, a seal member brought into slide contact with the track rail is provided on a periphery of the slider so as to eliminate the foreign substance adhering to the surface of the track rail when the slider moves. However, in a case where the rail mounting hole is provided in the track rail, the foreign substance enters the inside of the slider through the rail mounting hole, so an effect of the seal member is deteriorated. Further, the seal member comes into contact with the surface of the track rail with a certain level of fastening force, so in the case where the rail mounting hole is provided, there is a problem in that a leading end of the seal member is rubbed against an opening edge of the rail mounting hole, thereby causing the seal member to be deteriorated at an early stage.
Accordingly, in a case where the linear guide device is used under an environment in which the foreign substance easily adheres to the track rail, there is adopted a measure in which, after the track rail is mounted to the base portion by the fixing bolts, a closing caps are adapted to the rail mounting holes of the track rail, thereby closing the rail mounting holes. The closing cap is fitted into the large diameter portion so as to cover the head portion of the fixing bolt accommodated in the large diameter portion of the rail mounting hole, and the closing cap is flush with the surface of the track rail.
As the closing cap, a metal closing cap is disclosed in JP 2002-48138 A. The closing cap is composed of a fitting portion press-fitted into the large diameter portion of the rail mounting hole and an introduction portion inserted into the rail mounting hole before the fitting portion. The fitting portion has a press-fitting interference and is formed to have a larger outer diameter than the inner diameter of the large diameter portion of the rail mounting hole. By being applied with an external force from above by using a tool such as a hammer, the fitting portion is press-fitted into the large diameter portion of the rail mounting hole. Further, the fitting portion has a plurality of clearance grooves formed therein. The clearance grooves serve to mitigate stress caused by the press-fitting. The introduction portion is formed in a columnar shape having an outer diameter slightly smaller than the inner diameter of the large diameter portion of the rail mounting hole. The introduction portion is inserted into the rail mounting hole before the press-fitting of the fitting portion, thereby preventing the closing cap from being press-fitted into the rail mounting hole while being inclined.
Patent Document 1: JP 2002-48138 A